For better understanding of the present invention, a typical conventional nose bar device as applied to a rotary veneer lathe will be described with reference to FIGS. 1 and 2. It is to be understood that in describing the drawings only those portions of the construction of the veneer lathe has been shown which enable those skilled in the art to readily understand the underlying principle and concept of the present invention.
The veneer lathe includes a veneer peeling knife 5 having at its tip end a cutting edge 5a and fixed in a well-known manner to a knife mounting block 3 which forms a part of and is movable with a knife carriage of the lathe. The lathe further includes a block 9 which also forms a part of the knife carriage and to which a number of nose bars 7 (only one being shown) are fixedly mounted by means of bolts 10 at a predetermined interval along the cutting edge 5a of the veneer knife 5. Each nose bar 7 includes an upper base portion 7afixed to the nose bar mounting block 9 and a free end portion having at its lower end a pressure portion 8 In the form of an insert which is made of hard and wear resistant material and fitted to the tip end of the nose bar 7. Reference symbol 8a designates the front edge of the insert 8. The nose bar mounting block 9 is adjustably movable independently of the knife carriage in the double-headed arrow direction for positioning the front edge 8a of the pressure portion 8 with respect to the cutting edge 5a of the knife 5 so as to determine the distance therebetween in dependence on the thickness of wood veneer sheet to be peeled from a log by the knife 5.
It is noted, however, that the respective nose bars 7 are not necessarily identical in their dimensions or shape because of errors in accuracies of finished nose bars and their associated parts, as well as errors which occur in assembling or mounting these parts. In other words, the front edges 8a of the respective nose bars 7, when fixed to the nose bar mounting block 9, may not lie precisely on a straight line parallel to the cutting edge 5a of the veneer knife 5. When the mounting block 9 carrying the nose bars 7 is adjusted such that the front edge 5a of any one of the nose bars 7, which happens to be located closest to the cutting edge 5a of the knife 5, is brought just into contact with the cutting edge 5a as shown in FIG. 1, the front edges 8a of the other nose bars 7 may be then positioned clear of the knife cutting edge 5a, for example, as shown in FIG. 2. When the nose bar mounting block 9 is moved back for adjustment of the desired spaced distance between the nose bar front edges 8a and the knife cutting edge 5a, the distances between the knife edge 5a and the respective nose bar edges 8a may be varied from one nose bar 7 to another.
In practice of setting of nose bars 7, the nose bar mounting block 9 is adjusted and moved to a position where the spaced distance between the front edge 8a of the nose bar 7 and the cutting edge 5a of the knife 5 is slightly smaller than the desired thickness of veneer sheet to be peeled by the lathe, for example, about 90% of veneer sheet thickness, thus the nose bars 7 are disposed to press against the log for a distance corresponding to about 10% of the veneer sheet thickness. When the nose bar mounting block 9 is adjusted such that a nose bar 7 having a pressure portion 8 whose front edge 8a is located closest to the knife cutting edge 5a is set according to the above practice, the remaining nose bars 7 are spaced from the cutting edge 5a at a distance greater than 90% of the veneer thickness. In such a nose bar setting, the peeler log may be pressed insufficiently in the region thereof where the nose bars 7 are located too far from the knife cutting edge 5a, so that the resulting veneer sheet may be formed with relatively large and hence harmful checks or cracks and rough surfaces. Apparently, this will invite poor quality of veneer sheet.
On the other hand, if the nose bar mounting block 9 is adjusted such that a nose bar 7 having a pressure portion 8 whose front edge 8a is located farthest from the knife cutting edge 5a is set according to the above practice, nose bars 7 other than the above farthest one will be spaced from the cutting edge 5a by a distance less than 90% of the veneer sheet thickness. In such a case, the peeler log may be pressed excessively In the region thereof where the nose bars 7 are located too close to the knife cutting edge 5a with the result that the resulting veneer sheet may be formed partially thinner than desired, thus rendering the veneer sheet quality unacceptable. In a worse case when the space between the nose bar front edges 8a and the knife cutting edge 5a is too tight, a a veneer sheet just cut by the knife may fail to pass successfully through space and, therefore, be damaged or broken. As a result, veneer yield will be reduced remarkably and veneer quality seriously degraded.
Importantly, it is to be noted that such problems become noticeable, in particular, when producing a relatively thin veneer sheet. In peeling a sheet having a thickness of, for example, about 0.3 mm in the setting of about 0.27 mm of edge-to-edge distance corresponding to about 90% of veneer sheet thickness, the pressing amount which corresponds to 10% of the thickness, will be only about 0.03 mm. Apparently, the peeler log for such thin veneer sheet tends to be pressed either only very little or excessively depending on its locations. Thus, the prior art nose bar device has been unable to cope with the problems which occur in cutting a thin veneer sheet.
The problems may be solved to some extent by improving the machining accuracies of the knife mounting block 3, nose bar mounting block 9, nose bars 7 and their inserts 8, but only at the sacrifice of Increased of cost of the nose bar device and its related parts of the veneer lathe.
In a veneer lathe of the type which has a pair of spindles between which a peeler log is supported and driven, the log may hit part of the nose bars 7 while it is being loaded between the spindles. In such a case, the hit nose bars 7 may be deformed such that their lower free end portions are bent away from the knife cutting edge 5a. Such deformed nose bars 7 will cause the problems as referred to above.